1. Field of the Invention
The present invention relates to the field of computer systems. More specifically, the present invention relates to the operation of audio peripherals.
2. Background Information
Sounds can be recorded and manipulated by electronic systems by first converting sound waves into corresponding electrical impulses, then using electronic circuitry to store or modify these impulses. After modification and/or storage, the electrical impulses are converted back into sound waves. For example, in a basic, analog amplification system, a microphone converts sound waves (air compression waves) into voltage signals whereby the louder the sound the greater the voltage and the greater the sound wave frequency the greater the voltage frequency. This audio signal, which now corresponds to the original sound wave, is then run through circuitry to increase the voltage amplitude. Finally, this amplified audio voltage signal (or its associated current signal) is fed into a speaker which reconverts the audio signal back into sound waves which are louder than the original sound waves picked up by the microphone.
In the analog circuitry used in the amplifier example described above, the amplitude and frequency of the audio signals manipulated by the circuitry is directly related to the amplitude and frequency of its corresponding sound wave. One problem with modifying audio signals using analog circuitry is that a significant amount of noise tends to be added to the signal by inherent non-linearity of the transistors and other electronic components in the circuit.
In contrast, digital audio signals are represented by discrete digital samples of the analog audio signal, creating a stream of individual numbers which effectively "describe" the audio signal. Digital audio signals are modified using digital circuitry, the advantage of which is that non-linearity of the transistors in the circuit will not introduce noise to the audio signal because the transistors are not operated in their linear region. Instead, the sound quality of digitally manipulated audio signals is more a function of the sampling frequency and the maximum value (or bit length or resolution) of the audio signal samples. In addition, dealing with digital rather than analog audio signals can be advantageous because digital audio signals are compatible with digital electronic systems such as, for example, personal computers, thereby allowing a user to apply the advanced interfaces and processing power of these devices to audio signal processing.
Prior art computer system audio interfaces typically contain both the analog as well as digital circuitry. As such, the application specific integrated circuits (ASICs) used to implement these audio interfaces typically contain the digital circuitry necessary to support bus mastering and slave operation in accordance with a bus protocol, as well as the digital circuitry necessary to control analog circuit functions and to perform digital signal processing. Additionally, these audio interfaces also include the analog circuitry necessary to support analog audio signal exchange with a number of audio peripherals, such as microphone, CD player, modem, headset, and speaker, as well as any analog signal processing circuitry to support, for example, analog mixing, amplification, and filtering. As stated above, analog circuitry can add a significant amount of noise to an audio signal due to inherent limitations of the circuit components themselves when operated in their linear range. Because of this, special care must be taken and special materials are used to fabricate the analog circuitry of these audio interface ASICs, so that the circuit components are of high quality and contribute as little noise as possible to the analog audio signal.
Because these audio interface ASICs comprise a significant amount of both analog and digital circuitry on a single IC, the special fabrication process used to manufacture the analog circuitry of the device is also used to manufacture the digital circuitry of the device. As stated above, digital audio signal noise is more a function of sampling frequency and bit length rather than digital circuit component quality. Therefore, expensive fabrication costs associated with creating high quality analog circuitry for audio interface ASICs is effectively wasted on the digital circuitry of the device, thereby increasing the cost of the overall device and significantly limiting the size, complexity, and device density of the digital circuitry.
In copending U.S. patent application Ser. No. 08/673,282, entitled "Audio Serial Digital Interconnect", filed on Jun. 28, 1996, and having common inventorship as well as assignee with the present invention, a split architecture employing a digital controller and an analog audio interface packaged in separate ASICs, including an interconnect approach for interconnecting the two components, was disclosed. It is desirable that both the digital controller and the analog audio interface can be manufactured by a large number of different vendors. In other words, it is desirable that audio peripherals of a computer system may be operated through a digital controller manufactured by any one of a number of manufacturers, in conjunction with an analog audio interface manufactured by the same or any one of a number of other manufacturers.